Engine systems of this type are known for use as propellers or jet engines in aircraft and ships. With propellers or jet engines, a fluid having the mass m is sucked in at the velocity w in opposition to the desired direction of movement of the body to be propelled, the relative velocity of flow of the fluid through the propeller or the jet engine is increased to the velocity c, and the fluid is ejected at the relative velocity c (relative to the propeller or jet engine) in opposition to the direction of movement of the body. That is, the impulse of the fluid flowing through the body is varied within the body as to its magnitude. Thus, a stabilizing force acts on the body and as a reactive force is directed against the force variation at the fluid and therefore acts in the direction of movement of the body. The force magnitude in the direction of movement is I=m(c-w). For rockets, the force is generated by ejection at the velocity c of a medium that is carried along. The force magnitude therefore is I=m.multidot.c.
In drive systems of this type the level of the maximum impulse at low velocities is hardly above the force at higher velocities. For propellers and jet engines, the increase of the body velocity v is accompanied by an increase of the inflow velocity w. Thereby the specific force per kg of medium throughput is decreased. But with increasing velocity v, the dynamic pressure forward of the engine and thus the outflow velocity c will also increase, and the throughput of the mass m will also increase, so that on the whole the thrust remains more or less constant. For rockets, the constancy of the propulsive force can be taken direct from the formula.
The effect of transmissions is known in relation to vehicle drive systems. By means of the transmissions it is possible at low speeds to increase the maximum output torque at the wheels, whereby the propulsive force and the accelerating ability are improved while the amount of energy consumed is reduced.
It is the object of the invention to permit an increase in the propulsive force at low speeds also for drive systems of the kind which operate with a force variation of a sucked-in and ejected fluid.